Sub-ducting apparatus

ABSTRACT

A sub-ducting apparatus comprising a sub-duct, and a remotely operable path-finding head for facilitation of the subduct into a duct. The head is detachable at the end of the subduct and includes an expandable portion or a cutter, as a result of which, twisted or jammed cables may be removed from the duct.

This application is the US national phase of international applicationPCT/GB03/01278 filed 25 Mar. 2003 which designated the U.S. and claimsbenefit of EP 02252379.9, dated 2 Apr. 2002, the entire content of whichis hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a sub-ducting apparatus and a method ofsub-ducting, and more particularly to a system for accessing cables orother objects in a duct, for installation or removal thereof.

BACKGROUND AND SUMMARY

Telecommunications cables are often located in underground ducts thatare accessible at ground level at access points along the length of theduct. Redundant cables can be jammed in the ducts either by becomingadhered to the duct or by having subsequently installed cable twistedaround them. Until now, removal of the cables has been facilitated byapplication of a tensile force to the cable, which might, in some cases,free a jammed cable and allow its extraction. However, if the cablecannot be easily extracted in this way, applying tensile force candamage the duct and/or the other cables within the duct, resulting incostly and time-consuming repair work or even discarding of the damagedcables and/or duct. Removal of redundant cables reclaims valuable ductspace that can then be used to install new cables. The high cost ofinstalling new ducts can be delayed if optimal use is made of the ductspace.

It is an object of the present invention to alleviate these problems ina simple and effective manner. The invention is as stated in theappended claims. An advantage of using a path-finding element is thatjammed cables can be eased and separated away from other cables or fromthe duct without damaging the other cables or the duct itself. Anadditional advantage is that there is significantly less risk ofbreaking the redundant cable. The path-finding element or head isremotely operable such that it may be controlled from outside the ductto negotiate the obstructions it encounters inside the duct. Longerlengths of duct are accessible than would be without the head. Thepath-finding head may be detachable so that a head may be removed andchanged, such that the appropriate head for the particular job concernedcan be attached. The head may be outwardly deformable, so as to expandand gently push cables or other obstructions out of the way withoutdamaging them. The head may include a seal activated by pressurisationof the sub-duct. The seal enables the trapping of gas inside the head soas to facilitate the expansion of the deformable head.

The head may include a cutting portion at its front end, allowing thehead to cut through an obstruction or enable the release of a cable thathas become adhered to the duct.

The cutter may be a chisel head cutter for chiselling through small gapsbetween cables or between the cable and the duct, allowing gentlecutting or displacement of the obstruction.

The cutter may be a rotational cutter for cutting through obstructionswhere required. The rotational cutter is activated by relative movementof the sub-duct and the cutter. A helical thread translates linearmovement of the sub-duct to rotational movement of the cutter. In thismanner a rotational cutting action may be achieved simply andeffectively by a reciprocating motion of the sub-duct.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained in more detail by thefollowing non-limiting description of a preferred embodiment and withreference to the accompanying drawings, in which:

FIGS. 1A and 1B are schematics of an end view of a duct containingcables, illustrating the purpose of the invention;

FIG. 2 is a perspective view of an embodiment of the invention inoperation;

FIGS. 3A and 3B are schematics of a first path-finding head according tothe invention;

FIGS. 4A and 4B are schematics of a second path-finding head accordingto the invention;

FIG. 5 is a schematic of a third path-finding head according to theinvention; and

FIGS. 6A and 6B are schematics of a fourth path-finding head accordingto the invention.

DETAILED DESCRIPTION

FIG. 1A shows an end view of a duct 1 containing a plurality of cables2, and indicating a cable to be removed 4. FIG. 1B shows the same ductfrom the other end. Cables 2 have been twisted and the cable to beremoved 4 is intertwined between other cables. The duct 1 is locatedunderground and is accessible at ground level at access points along thelength of the duct. The access ports are generally spaced up to 250 mintervals. The sub-ducting apparatus 10 is thus required to enablesub-ducting operations to be conducted over this distance, withoutdamaging the other cables 2 in the duct or the duct 1 itself.

The sub-ducting apparatus 10 consists of a length of sub-duct 12 and oneor more detachable heads 20. Additional equipment includes a drum 14, alinear engine 16, and a compressor 18. FIG. 2 shows the sub-duct 12wound onto the drum 14, positioned nearby an access point 22. Thesub-duct is an elongate sleeve manufactured from polyethylene or othersimilar material. FIG. 2 shows a sub-duct having a circularcross-section, however other cross-sections of sub-duct may be used. Thesub-duct 12 bore is preferably slightly larger than that of theredundant cable 4 to create a clearance gap so as to minimise frictionsuch that the sub-duct 12 may be sleeved over the cable 4. The drum 14is preferably portable and contains a length of sub-duct 12 wound aroundit. The free end of the sub-duct 12 may be advanced towards the duct andthrough it by a linear engine 16. The engine may have a guide portion 17for guiding the sub-duct into the duct 1.

The path-finding elements 20 are heads that can be detachably fitted atthe end of the sub-duct 12. There may be several different types ofpath-finding head, each designed to perform a task to ease, cut, orotherwise negotiate a path through the obstruction in the duct.

Path-finding head 20A may be utilised for easing a path through twistedor jammed cables 2 such that the cables 2 do not become damaged. As seenin FIG. 3A, the head is deformable and is detachably fixed to thesub-duct 12. The deformable head 20A is preferably manufactured from ahardwearing, flexible and elastic material. The head 20A forms a sleeve,through which the cable 4 extends. The sleeve 20A profile shown in FIG.3A and FIG. 3B would be optimised to perform its task and is illustratedfor example only. The sleeve 20A profile U-turns in on itself such thatthe end 30 of the sleeve faces back down the sub-duct, producing arounded front 32 to the head 20A. The profile is designed such thatwhilst the sub-duct 12 is advanced along the cable 4, the flexible headis not in contact with the cable 4, allowing the duct to pass over thecable with minimum friction. However, in the event of finding anothercable 2 obstructing the path of the advancing sub-duct 12, the head canbe pressurised to expand as shown in FIG. 3B. Compressed gas from thecompressor 18 is fed through the sub-duct 12 and into the path-findinghead 20A. The expansion of the head 20A is facilitated by the sleevebending outward such that the sleeve end 30 contacts and creates a seal34 against the cable 4. The pressurised seal 34 enables the expandedhead 20A to gently force the cables 2 away from the cable 4 allowingfurther advancement of the sub-duct 12 where known prior art methods ofcable removal require brute force to be applied to unjam or untwist thecables 2. The path-finding head 20A therefore minimises or eliminatesdamage to the cables 4.

Path-finding head 20B, seen in FIG. 4A also includes a pressure seal 40.The head 20B comprises an expandable section 42 and a front portion 44.The expandable section 42 is located behind the front portion 44. Thefront portion 44 comprises a chisel portion 46 manufactured from rubber,inside of which is a rubber ring 50. The rubber ring 50 is unattached tothe head 20B. At the base of the rubber chisel portion is a shoulderportion 48 forming an annulus of rubber material of thickness greaterthan that forming the chisel portion 46. When the head 20B is fitted tothe sub-duct 12 and sleeved over a cable 4, the rubber ring 50 istrapped in the chamber 45 formed between the rubber chisel head 46 andthe cable 4, and is prevented from leaving the chamber 45 by shoulderportion 48. The pressure seal 40 of head 20B is activated bypressurisation of the sub-duct 12, preferably by application of acompressed gas through the sub-duct 12 and into the head 20B. FIG. 4Bshows the head 20B after pressurisation of the sub-duct 12 and head 20B.The expandable section 42 deforms outwardly, decreasing the overalllength of the head 20B. The front portion 44 is hence retracted towardsthe sub-duct 12, decreasing the width of the gap in which the rubberring 50 is trapped, until the rubber chisel head 46 and rubber ring 50come into frictional contact to create the pressure seal 40. The head20B has the advantage that the expandable section 42 eases cables awayfrom the cable 4, and the rubber chisel portion 46 can chisel throughsmall gaps between obstructing cables 2.

Path-finding head 20C is shown in FIG. 5. The head consists of a chiselcutter manufactured from tool steel or similar hardwearing toolmaterial. In use, the head 20C surrounds the cable 4 and the chiselcutter may be employed for freeing a cable 4 that has adhered to theduct, by chiselling between the cable 4 and duct 1. The chiselling isachieved by applying a force to the sub-duct 12 at the access point 22.In some situations, reciprocating movement of the chisel head 20D may benecessary to provide effective chiselling, and may be achieved by areciprocating movement of the subduct. Path-finding head 20C may also besuitable for guiding the sub-duct 12 through small gaps between cables2.

Path-finding head 20D shown in FIGS. 6A and 6B, comprises a rotationalcutter 60 at the front of the head. The rotational cutter 60 iscylindrical and manufactured from tool steel or other such hardwearingtool material, and includes a ring of teeth 62 at the front thereof. Theteeth 62 of the cutter 60 therefore face the direction of sub-ductadvancement. Extending rearwardly from the rotational cutter 60 is adouble sleeve portion 64 having an inner sleeve 66 and an outer sleeve68, extending away from the rotational cutter 60. A third sleeve 70 isinsertable into the double sleeve 64. A helical thread 75 is formed onthe surface 73 of the inner sleeve 66 and a lug on the inner surface 71of the third sleeve 70 projects into it. A helical spring 77 is coiledaround the inner sleeve 66 such that it occupies the gap between theinner sleeve 66 and the outer sleeve 68, and biases the third sleeve 70away from the cutter 60.

In use, the third sleeve 70 is attached to the sub-duct 12. The cable 4passes through the inner sleeve 66 and through the rotational cutter 60.FIG. 6A shows the head 20D attached to the sub-duct 12. Whilst thesub-duct 12 is advanced along the cable 4, the spring 77 is relaxed. Inthe event of requiring the cutter 60 to cut away an adhered or jammedcable 4, a force must be applied to the sub-duct 12 to producereciprocating movement of the sub-duct 12. The linear motion of thesub-duct 12 transfers the motion directly to the third sleeve 70, andthe engagement of the lug with the helical thread 75 ensures that as thethird sleeve 70 advances, the inner sleeve 66 rotates, thus rotating thecutter. Cutting takes place during the advancement of the head 20D. Theadvancing third sleeve 70 compresses the helical spring 77 as shown inFIG. 6B. Releasing the force applied to the sub-duct 12 releases thespring 77 and the mechanism returns to rest as shown in FIG. 6A. Cuttingceases during retraction of the head 20D. Repeatedly applying andreleasing force on the sub-duct 12 hence provides an intermittentrotational cutting motion. This could be achieved manually, but could bemore effective if applied with a pushing machine (not shown). Thus anadvantage of path-finding head 20D is that linear motion is translatedvia the helical thread 75 to rotating motion so as to facilitate therotational cutter 60. Compressed gas may be applied to the obstructionwhilst using the cutting heads 20C and 20D to assist removal of theobstruction.

Operation of the sub-ducting apparatus 10 involves unwinding thesub-duct 12 from the drum 14 and feeding it into the duct 1. Thesub-duct 12 is pushed, or sleeved, over and along the redundant cable 4.The sub-duct 12 may be pushed in by hand or with the assistance of thelinear engine 16. It is recommended that the duct be surveyed forpotential obstructions as much as possible prior to the insertion of thesub-duct 12, in order to assess which type of path-finding head 20 willbe required to overcome the obstruction. The path-finding head 20 maythen be activated as necessary, for instance by applying a force to thesub-duct 12 or by applying a compressed gas from the compressor 18 atthe access point 22 through the access point end of the sub-duct 12.Once the obstructing cable 2 has been eased or unjammed, or the cable 4has been freed from the duct 1, and the sub-duct 12 reaches the end ofthe redundant cable 4, the cable 4 is pulled out. If this proves to bedifficult, compressed gas may be applied again at the access point 22 toassist removal of the cable 4. Once the cable 4 is removed from the duct1, the sub-duct 12 may be cut and left in the duct 1 for use as asub-duct, or it may be used to pull in another cable. Thus thesub-ducting apparatus 10 may be used to install new cables.

The sub-ducting apparatus may also be used for installation ofsub-ducts. Established sub-duct installation methods require a length offlexible rod to which a rope is attached to be inserted into the duct.The sub-duct is attached to the end of the rope, and pulling the ropepulls the sub-duct into the duct. However the path-finding heads 20A and20B of the present sub-ducting apparatus can be used to ease cables outof the way in a crowded duct. This would enable a sub-duct to beinstalled where the friction between the sub-duct and any twisted cableswould prevent the utilisation of established sub-duct installationmethods.

Where a path-finding head is not required, a metallic sub-duct protector80, seen in FIG. 2, may be attached at the advancing end of the sub-ductso as to avoid damage to the end of the sub-duct or to other cables.

It will be understood by the person skilled in the art that anyappropriate materials may be used for the sub-duct apparatus components.The sub-ducting apparatus can be used to remove or install cables or forinstalling sub-ducts. The invention may apply to types of cable otherthan telecommunications cable. Other types of cutting and easing headsmay be used as part of the sub-ducting apparatus. The linear engine mayinclude any type of engine or motor.

1. A sub-ducting apparatus for removing from a duct a cable which isjammed within the duct by an obstruction, comprising a sub-duct and aremotely operable path-finding element comprising easing means and/orcutting means, in use arranged to negotiate a path around or through theobstacle, whereby the sub-duct is inserted into the duct over the jammedcable.
 2. An apparatus as claimed in claim 1 in which the sub-duct is anelongate sleeve.
 3. An apparatus as claimed in claim 1 wherein thepath-finding element is a path-finding head.
 4. An apparatus as claimedin claim 3 wherein the head is detachable.
 5. An apparatus as claimed inclaim 4 in which the head includes a seal activated by pressurisation ofthe sub-duct.
 6. An apparatus as claimed in claim 3 in which the head isoutwardly deformable.
 7. An apparatus as claimed in claim 6 in which thehead is outwardly deformable at the front end.
 8. An apparatus asclaimed in claim 6 in which the head is outwardly deformable at aportion set back from the front end.
 9. An apparatus as claimed in claim1 in which the head has a cutting portion at the front end.
 10. Anapparatus as claimed in claim 9 in which the cutting portion is a chiselportion.
 11. An apparatus as claimed in claim 9 in which the cuttingportion is a rotational cutter.
 12. An apparatus as claimed in claim 11in which the cutter is activated by relative movement of the sub-ductand the cutter.
 13. An apparatus as claimed in claim 12 in which ahelical thread translates linear movement of the sub-duct to rotationalmovement of the cutter.
 14. An apparatus for advancing a sub-duct into amain duct comprising apparatus as claimed in claim 1 and means foradvancing it.
 15. An apparatus according to claim 1 in which thesub-duct is inserted into the duct so that it sleeves over a cablewithin the duct for subsequent removal of the cable from the duct.
 16. Amethod of removing from a duct a cable which is jammed within the ductby an obstruction, comprising inserting a sub-ducting apparatus into theduct over the jammed cable, the sub-ducting apparatus comprising asub-duct and a remotely operable path-finding element comprising easingmeans and/or cutting means, and remotely operating the path-findingelement to negotiate a path around or through the obstacle, whereby thesub-duct is inserted into the duct over the jammed cable.
 17. A methodaccording to claim 16 in which the advancement of the sub-duct so thatit sleeves over a cable within the duct for subsequent removal of thecable from the duct.